About one-third of the population of the developed world is destined to die from cancer. Current treatment for cancers—including chemotherapy and radiotherapy—are based on killing cancer cells preferentially to normal cells, the so-called “therapeutic window” which accepts significant adverse effects for even marginal slowing of tumor growth. Specific treatments that spare normal cells are urgently needed.
Cancer cells are different from normal cells in many ways, including a propensity for protein misfolding, intracellularly and at the cell surface. Such misfolded proteins may be the consequence of germ cell or somatic mutation, chromosomal translocation or aneuploidy, mutagenic effects of chemotherapy or radiation therapy, titration of chaperones, molecular crowding in the endoplasmic reticulum and other secretory compartments including the cell surface, aberrant glycosylation and trafficking, impaired clearance and/or degradation, environmental stressors or allosteric influences relevant to the tumor bed (such as lowered pH or increased ligand concentration), and post-translational modifications including oxidation and nitration of select residues. All or some of these factors relevant to cancer contribute to greater dynamic fluctuation and net solvent exposure of specific regions of proteins which are normally rarely accessible in non-cancerous cells. Antibody recognition of these abnormally exposed protein motifs, designated Disease Specific Epitopes (DSE), will serve as a diagnostic cancer marker or cancer treatment target, and provide insight into abnormal cell growth in cancer and other diseases.
A disease specific epitope for the prion protein (PrP) has recently been described as a diagnostic and treatment target for the transmissible spongiform encephalopathies (Paramithiotis et al, Nature Medicine 2003, 9(7):893). This prion DSE, defined by the core trimer YYR, is an epitope exposed on the molecular surface of disease-misfolded PrPSc, but is buried in the antibody-inaccessible interior of the normal prion protein PrPC. PrPC is abundantly expressed by normal circulating lymphoid and myeloid cells (Cashman et al, Cell 1990, 61(1):185), and plays a role in hematopoietic differentiation from CD34+ bone marrow stem cells (Dodelet and Cashman, Blood 1998, 91(5):1556). However, YYR surface immunoreactivity had never been detected on any normal cell, including splenocytes of mixed lineage, and dissociated brain cells.
US 2009/0175884 establishes that certain cancer cells are reactive with antibodies raised against the YYR epitope unique to the misfolded form of PrP, and proposes the use of YYR antibodies to inhibit the growth and/or proliferation of those cancer cells. The production of YYR antibodies and their use to control progression of PrP aggregation, as a way of treating transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease (CJD) was first described in U.S. Pat. No. 7,041,807. WO 2010/099612 identifies and proposes the targeting of another cryptic epitope that is exposed when PrP misfolds, i.e., the trimer YML. Also, WO 2010/04020 describes an algorithm useful to predict misfolding “hot spots” in a variety of target proteins, including PrP. Those inventors suggest targeting the predicted disease specific epitopes using antibodies, for instance, as a means for treating diseases in which the misfolding of that target protein is implicated.
It is an object of the present invention to provide antibodies, and fragments and conjugates thereof that bind selectively to a misfolded form of PrP.
It is a further object of the present invention to provide such antibodies, fragments and conjugates as compositions, particularly for therapeutic and diagnostic use.
It is a further object of the present invention to provide a method useful, in a subject in need thereof, to control the growth and/or proliferation of disease cells that present misfolded PrP on their surface.
It is a further object of the present invention to provide a method useful, in a subject in need thereof, to control the progression of PrP aggregation, as a means of treating diseases in which aggregation of PrP is implicated, such as the transmissible spongiform encephalopathies.